1. Field of the Invention
The present invention relates in general to wireless communication systems and components, and in particular to a printed circuit board configured dual-fed coupled stripline PCB dipole antenna.
2. Description of the Related Art
Communication system designers are constantly seeking ways to improve the performance of system components and signal processing circuits, but without substantially increasing complexity of hardware or costs. For example, designers always want received and transmitted signals to be stronger. Almost all conventional antennas have had either only one plane (XZ-plane or YZ-plane or XY-plane) with significant polarization energy, or a complicated or excessively large structure.
A conventional sleeve antenna comprises a radiation element having an electrical length of one quarter wavelength, a sleeve having an electrical length of one quarter wavelength, and a coaxial cable for feeding electric power to the radiation element. An outer conductor of the coaxial cable is connected to the sleeve, while an inner conductor of the coaxial cable is connected to the radiation element.
A conventional inverted coaxial dipole antenna has a central conductor of a coaxial cable connected via a feeding line to a sleeve, wherein the feeding line is extended through a slot which is formed in an outer tube of the antenna.
A conventional stripline antenna is shown in FIG. 4. The antenna comprises a coupler 70, a radiation element 72 spaced apart from but adjacent the coupler 70 and serving as an antenna element, a dielectric substrate 75 on which the antenna element is disposed, a ground plane 74 under the dielectric substrate 75, a feed point 71 on the coupler 70, and a short point 73 disposed on the radiation element 72 and shorted to the ground plane 74.
Conventional antennas such as those described above have a number of disadvantages.
Conventional sleeve antennas and inverted coaxial dipole antennas involve complicated fabrication and adjustment, because the feeding coaxial cable is connected to the sleeve. This makes quality control in manufacturing difficult.
Stripline or microstrip antennas can solve the above problems associated with conventional sleeve antennas and inverted coaxial dipole antennas. However, the polarization energy of stripline or microstrip antennas is significant in only one plane (XZ-plane or YZ-plane or XY-plane), and is minimal or even faded in the other two planes. Additionally, the intensity of the utilized polarization energy changes with the orientation of the antenna. Thus optimum radiation efficiency may not be always achieved. For documentation that describes and illustrates conventional antennas, attention is directed to U.S. Pat. No. 4,069,483 and Taiwan Patent Application No. 87112281.
U.S. Pat. No. 4,833,482 discloses a circularly polarized microstrip antenna array which comprises two independent linearly polarized arrays. The first and second antenna arrays are fed with two independent signals about 90 degrees apart, and independently radiate a horizontally linearly polarized wave and a vertically linearly polarized wave respectively. Far afield, these waves become a circularly polarized wave. Each antenna array also has a plurality of stripline conductors having a plurality of radiation elements protruding outwardly therefrom in a direction of about 45 degrees from the stripline conductors. This antenna arrangement, however, is difficult to manufacture and increases production costs. Moreover, the stripline conductors disposed adjacent each other cause mutual interference, which reduces radiation efficiency. The copending application with an unknown serial number filed Mar. 5, 2001 with the title xe2x80x9cSTRIPLINE PCB DIPOLE ANTENNAxe2x80x9d having the same inventors and the same assignee with the instant application, discloses one approach to improve the aforementioned shortcomings.
A preferred embodiment of the present invention provides two dipole antenna elements that are arranged perpendicularly to each other to form a single antenna, a PCB on which the two dipole antenna elements are disposed, and two feeding lines connected with the two dipole antenna elements respectively. This perpendicular arrangement makes use of two planes of the XZ-plane, XY-plane and YZ-plane. The antenna obtains optimum polarization energy by selecting the strongest energy plane. This achieves maximized radiation efficiency under any particular orientation of the antenna. The strongest energy plane is selected by controlled switching, by means of dual-fed signal mode.
In order to effectively minimize interference, two T-shaped dipole arms of each dipole antenna element are disposed on opposite surfaces of the PCB. Such T-shaped configurations also make the antenna more compact.